This invention relates to a novel alloy for use in an environment exposed to radioactive rays, especially to the neutron rays, and more specifically to austenite steel for use in a nuclear reactor and reactor core members.
Reactor core members such as core supportors, a core shroud, control rods, etc. disposed inside a nuclear reactor are used while being exposed to the neutron radiation. When they received the neutron rays, there takes place damage to materials due to the neutron radiation, whereby they markedly change their characteristics. Deterioration of the material characteristics exerts critical influences upon the safety the reliability of the reactor. Therefore, the reactor core member material must be selected taking such things into account.
In light-water reactors, it is feared that the material of internal instrument and appliance would undergo radiation-embrittlement during operation due to the neutron radiation. Besides embrittlement due to the neutron radiation, an SCC phenomenon in water at high temperature and high pressure must also be taken into account in selecting the material for the core.
In fast breeder reactors, damage to a fuel covering tube, a core tube or the like has specifically been a critical problem. In this reactor, the temperature of the coolant (liquid sodium) is relatively high, e.g., 350.degree. to 500.degree. C., and moreover, the amount of high speed neutron radiation is by far greater than in the light-water reactors. Therefore, voids occur on the material exposed to the neutron radiation, thus causing a serious problem of swelling (of volume).
In fusion reactors, the neutron radiation in such high energy as to be incomparable to that in fission reactors would take place. Hence, a first wall material encompassing the plasma is exposed to severe radiation damages. In this instance, damage due to gas atoms (hydrogen and helium atoms) generated by the nuclear conversion becomes an extremely critical problem, in addition to the abovementioned swelling phenomenon.
As for swelling prevention of the core material exposed to neutron rays, there are various proposals. For example, in Japanese Laid-open Patent Application No. 54-36498, austenite stainless steel including titanium, niobium and carbon is disclosed, and in Japanese Laid-open Patent Application No. 54-84197, there is disclosed a method of treatment of austenite stainless steel, wherein the austenite stainless steel is subjected to solid solution treatment at a temperature from 950.degree. to 1200.degree. C. after being finally formed, and after then, to aging treatment at a temperature of about 600.degree. to 800.degree. C. for about 50 hours.